title: Impact of hip fracture on mortality: a cohort study in hip fracture discordant identical twins.
abstract: Several studies have shown a long-lasting higher mortality after hip fracture, but the reasons for the excess risk are not well understood. We aimed to determine whether a higher mortality after hip fracture exists when controlling for genetic constitution, shared environment, comorbidity, and lifestyle by use of a nationwide cohort study in hip fracture discordant monozygotic twins. All 286 identical Swedish twin pairs discordant for hip fracture (1972 to 2010) were identified. Comorbidity and lifestyle information was retrieved by registers and questionnaire information. We used intrapair Cox regression to compute multivariable-adjusted hazard ratios (HRs) for death. During follow-up, 143 twins with a hip fracture died (50%) compared with 101 twins (35%) without a hip fracture. Through the first year after hip fracture, the rate of death increased fourfold in women (HR = 3.71; 95% confidence interval [CI] 1.32-10.40) and sevenfold in men (HR = 6.67; 95% CI 1.47-30.13). The increased rate in women only persisted during the first year after hip fracture (HR after 1 year = 0.99; 95% CI 0.66-1.50), whereas the corresponding HR in men was 2.58 (95% CI 1.02-6.62). The higher risk in men after the hip fracture event was successively attenuated during follow-up. After 5 years, the hazard ratio in men with a hip fracture was 1.19 (95% CI 0.29-4.90). On average, the hip fracture contributed to 0.9 years of life lost in women (95% CI 0.06-1.7) and 2.7 years in men (95% CI 1.7-3.7). The potential years of life lost associated with the hip fracture was especially pronounced in older men (>75 years), with an average loss of 47% (95% CI 31-61) of the expected remaining lifetime. We conclude that both women and men display a higher mortality after hip fracture independent of genes, comorbidity, and lifestyle.
authors.affiliation: Department of Surgical Sciences, Section of Orthopaedics, Uppsala University, Uppsala, Sweden; Uppsala Clinical Research Center, Uppsala University, Uppsala, Sweden.
authors.forename: Karl
authors.initials: K
authors.lastname: Michaëlsson
authors.forename: Peter
authors.initials: P
authors.lastname: Nordström
authors.forename: Anna
authors.initials: A
authors.lastname: Nordström
authors.forename: Hans
authors.initials: H
authors.lastname: Garmo
authors.forename: Liisa
authors.initials: L
authors.lastname: Byberg
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Pedersen
authors.forename: Håkan
authors.initials: H
authors.lastname: Melhus
mesh_terms: D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005500:Follow-Up Studies; D006620:Hip Fractures / Q000401:mortality*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012737:Sex Factors; D013548:Sweden / Q000453:epidemiology; D014430:Twins, Monozygotic
keywords: EPIDEMIOLOGY; GENETIC RESEARCH; HIP FRACTURE; MORTALITY; TWIN